A student society of undergraduates and PhD students dedicated to pushing the limits of high power rocketry and high altitude ballooning. We are based out of the Cambridge University Engineering Department and hold regular meetings.
A week later, and the balloon is still (at least partially) inflated.
Tasks for this week involve working out the optimal pressure for the HAB – too low and it won’t get off the ground, too high and it will leak under its own pressure. As the altitude increases pressure decreases rapidly, and at an altitude of approximately 13km the external pressure will be less than one fifth of that on the ground. Without pre-stretching the balloon and the right internal pressure, our project will not get very far off the ground!
Today we created our first (partially) working prototype of the balloon! The initial design for 4 semi-circular sections was quickly replaced with a 2-circle approach, where we cut out two one-meter diameter circles from our roll of plastic. This was because the extra work involved in welding 4 sections, combined with the welds being the weakest part of the balloon meant that there was no purpose in the extra effort involved.
We welded them together in tangential sections, eventually ending up with a mylar balloon shape. The plastic we were using was slightly damaged, meaning we had to re-weld some parts of it a few times, but at the end of today’s session we were able to fill up the balloon with air and leave it in the DPO for inspection next week – only time will tell if it has leaked!
Current radios on High Altitude Ballons (HABs) are laughably slow, on the order of 50 bits/s. While this can suffice for transmitting simple data strings such as GPS co-ordinates, it’s useless for anything else. There have been several attempts at in-flight image transmission for amateur HABs with existing radios, though these took around 6 minutes to transmit a single small grainy image.
Lynx is an experimental digital radio transmitter for HABs, capable of data rates an order of magnitude above existing amateur systems. The end goal of the project is to have a live video stream coming from a balloon in flight. It features a powerful ARM chip to deal with the error correction codes and signal processing.
This development board will allow a number of the key radio systems to be thoroughly tested before implementation in the first flight model. Currently, we are waiting for some RF components to arrive from the US before the board is assembled.
A while ago, the nice folks at Bronkhorst gave us a helium-compatible gas flow meter on loan. This shiny (literally) bit of kit allows us to deliver precise quantities of helium to our high altitude balloons, hopefully increasing the accuracy of our predictions. The flow meter needs control from a PC (with an RS232 port!), which is inconvenient when in the middle of a field.
Skunk is a project to use an Arduino as the controller for the flow meter, meaning we can put it all in a nice case with a battery and control panel for field-filling. A key part of this is the interface PCB – an Arduino shield with all the random circuitry crammed on. After a few weeks of design, the wonderful, amazing, people at the Cambridge Circuit Company fabricated a beautiful PCB for us – pictures of the bare and made-up boards are below! (Points for spotting the design mistakes I’ve had to correct – thankfully none were show-stoppers). There’s still a lot left to do on Skunk, but for once it’s making solid progress. One of our new members will be developing the firmware in the new year, once the hardware is all hooked up.
The PCBs for the second revision of the Joey-M flight computer have arrived from Cambridge Circuit company. This revision carries some minor fixes from the first as well as the addition of the new CUSF logo to the rear silkscreen.
Thanks once again to Cambridge Circuit Company for these fantastic boards.
NOVA21 went up at around 1330BST carrying JOEY-M, Squirrel (the Android project) and a special guest. It got to 27.2km altitude before burst, landing near Braintree.
The flight was mostly a test of the new Joey and Squirrel flight code. Joey performed well, though there was a lot of interference on the 433.8MHz frequency it was using, so later revisions will swap to a higher frequency. Squirrel was great up until around 8km when for a yet-unknown reason the flight software cut out, which meant the radio and camera were disabled. However, after landing we were able to reactive Squirrel remotely, getting some tweets of photos from the field it was in and its GPS position. The payloads were recovered successfully.
NOVA22 launched at around 1500BST carrying Wombat along with ASTRA from the University of Southamption with an experimental HF transmitter on 27MHz and a balloon neck flight computer with a differential pressure sensor to log the balloon’s pressure.
NOVA22 reached 21km before burst (on a smaller 350g balloon) and landed close to NOVA21. Wombat worked much better than on NOVA20, being successfully decoded by many people in the listener network. ASTRA’s experimental radio also worked, though unfortunately the payload lost GPS lock for a part of the flight. The balloon neck flight computer was a success, getting back valid pressure data for the balloon.